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Old 03-27-2011, 08:46 PM   #1
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30 amp male to 50 amp female adapter

Has any one experianced my problem? Had some extensive body work (wrecked by a drunk one night) done on my '92 Golf Stream and I thought they may have wire my gen set into the auto transfer switch wrong. Naw, not the case. Starting at the converter and working back to the transfer switch I had power to one side of the coach but not the other. Every thing woked fine with the gen set but only one side of the coach with shore power. After working a couple of hours this afternoon I found the problem. It's my 30 to 50 amp adapter plug I just bought. I guess they didn't put a jumper in the 50 amp side to supply power to both legs of the transfer switch. Is this a bad 30 to 50 amp adapter? Anyone?
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Old 03-28-2011, 03:47 AM   #2
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Hello Arnold and . We are glad to have you join us here and we look forward to reading of your adventures and experiences. I am sure you will enjoy the website and forums. Good luck, stay safe and keep us posted.
You are correct in that the 30 amp adapter plugged onto your 50 amp power cord is defective and is not connecting the other leg of the cord to power. Get a new adapter and I might also recommend a good Surge Guard type power supply protection for the shore power, if you do not have any already.
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Old 03-28-2011, 05:26 AM   #3
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Now.. I always thought that since 50amp was 240 volt (2 legs), and 30 was 120 volt (single leg), when you used a 30-50 amp plug, you WOULD lose one side. You are losing a 120 volt leg. Thats what the 30+20 to 50 adapters were for...

Now, there appears to be no rhyme or reason as to just which leg you will lose as that depends entirely on the little chinese lady who solders them. Some people take a ohm meter and test and get one of each, just in case.
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Old 03-28-2011, 05:26 AM   #4
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Has any one experianced my problem? Is this a bad 30 to 50 amp adapter? Anyone?
Yes, I've had the dogbone adapters fail, both in the "one leg" mode you describe as well as total failure where they wouldn't conduct power to either 50 amp leg of the RV.

Jim, if the 30 to 50 dogbones are working as designed, they jumper the 2 each 50 amp legs of the RV together in the dogbone and make them work as a single 30 amp leg.

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Old 03-28-2011, 05:37 AM   #5
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Jim, if the 30 to 50 dogbones are working as designed, they jumper the 2 each 50 amp legs of the RV together in the dogbone and make them work as a single 30 amp leg.

Rusty
Isnt that alittle scary? Makes it quite easy to overload the 30 amp...
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Old 03-28-2011, 05:51 AM   #6
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While being an European and cutomed to our easy way of power distribution,
I studied the US way of power. I found that:
A 50 Amp service is 2 lines of 110 volts each fused at 50 amps.
It can be that it are two same phase lines or 2 oposite phase lines.
If it is oposite phases, there is 220 volts between the 2 "hots". but still 110 between hot and neutral.
A 220 volt connector has 2 horizontal blades (in line) and is a whole different beast.
To get the most power into the RV, lacking 50 amp service is A 30 amp line for the main (household) circuit and a 20 amp for the secondary (the 2nd, 3rd and 4rth Airco).
Most Campground power poles have 30 and aditional 20 amp connectors. Hopefully each with its own fuse....
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Old 03-28-2011, 06:21 AM   #7
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Isn't that a little scary? Makes it quite easy to overload the 30 amp...
Jim,

When you are hooked to a 30 amp shore power connection, you are only able to use 30 amps of power. Some coaches with have an EMS distribution system wired into their coach to manage the 30 amps. It will shut down items when the coach has reached the 30 amps. For coaches without the EMS management system, then it is up to the user to manage how much stuff they are using making sure they don't over load the 30 amp circuit.

I guess if they were careless, the pedestal 30 amp breaker would eventually heat up and hopefully trip shutting off the power but there also could be other problems that may happen first.

People need to learn how to use their RVs properly without causing fires or problems.

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Old 03-28-2011, 06:54 AM   #8
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hmmmm, odd. I thought the power missing on one leg is how my ems knows I'm on 30 not 50 amps?
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Old 03-28-2011, 07:09 AM   #9
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hmmmm, odd. I thought the power missing on one leg is how my ems knows I'm on 30 not 50 amps?
Most look for 240VAC across L1 and L2 as an indicator for being connected to properly wired 50 amp 120/240VAC split phase service. If they don't see 240VAC, they assume that you're on 30 amps.

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Old 03-28-2011, 07:10 AM   #10
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Isnt that alittle scary? Makes it quite easy to overload the 30 amp...
At that point, the 30 amp shore power breaker on the pedestal is providing overcurrent protection.

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Old 03-28-2011, 07:13 AM   #11
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Isnt that alittle scary? Makes it quite easy to overload the 30 amp...

This is where common sense comes into play.
It's why alot of the adapters run hot or fail. People try to run everything in the coach and it trys to draw more than 30 amps and ends up heating up the adapter. The gauge wire used in the adapter is not adequate to handle the load and starts to heat up.

"hmmmm, odd. I thought the power missing on one leg is how my ems knows I'm on 30 not 50 amps?"

You are not missing power on one leg. Since a 50 amp coach basically uses two 120 circuits. Common neutral and one phase of the hot. Common neutral and the other phase of the hot ...

30 amp is just one hot and a neutral ( and ground ) so the adaptor takes that hot lead and splits it ( ties it together ) to the two hot leads going into the coach. You now have 30 amps avail for both sides of the coach's circuit.
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Old 03-28-2011, 07:53 AM   #12
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On a true 120/240 volt 3 pole 4 wire grounding split phase system the voltage between the postion X (L1) and Y (L2) in the picture will be 240 VAC. The voltage between X and W or X and G will be 120 VAC and the voltage between Y and W or Y and G the voltage will be 120 VAC. There should be zero voltage between G and W.On a FAKE 50 amp service the CG will use either L1 or L2 for X and Y. The voltage between X and Y in this case would be zero. The voltage between X and W or X and G will be 120 VAC and the voltage between Y and W or Y and G the voltage will be 120 VAC. There should be zero voltage between G and W. This type of 50 amp service will provide 6,000 watts, which is better than a 30 amps service which will provide 3,600 watts but it is not a true or correctly wired 50 amp service.
The 30 amp service is nothing more than a glorified 20 amp service. L1 = 120 volts, L2 = Neutral and a ground wire. The use of heavier wire and a larger breaker make this a 30 amp service.
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Old 03-28-2011, 08:36 AM   #13
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We can't control who does the wiring. I was in the business and I am always amazed at some of the wiring that got through inspection. Some journeymen never check on what was done by the helper. Or, in this case they may intentionally use one side of the phase to wire the box as a safety measure. Some coaches will use the 240 but they are not common so for the most part this would not be an issue.

edit to add: Speaking of unsafe practices I was in one campground where they had the triplex lying on the ground inbetween the transformer and the Distribution panel ... I was watching the guy cutting the grass near that .. plus you never know what young kids will do and in camp you have too many sharp implements .. could be a deadly combination


My previous post I technically use the word phase wrong as it is a single phase system, but for simplification purposes the word phase avoids confusion.
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Old 03-28-2011, 10:25 AM   #14
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Now.. I always thought that since 50amp was 240 volt (2 legs), and 30 was 120 volt (single leg), when you used a 30-50 amp plug, you WOULD lose one side. You are losing a 120 volt leg. Thats what the 30+20 to 50 adapters were for...
You are both right and wrong.. The reason for using 250 volt "DIVIDED" is very simply that it cuts down on the voltage drop.. I can give you more info on that if you need but think of it this way.

With a perfectly balanced system, (that is both legs carrying the exact same current) the neutral wire carries NOTHING, period, NOTHING, in practice it will never be exactly balanced but....

When you figure the voltage drop the current in one leg basically does not count.

So if you have 20 amps in one leg, and 25 in the other, Your voltage drop is LESS than if you had 45 amps on a 120 volt line. (It's less than even the 25 amps but this gets very complex)

NOTHING in the RV should REQUIRE 240 volts, Everything is 120 volt, Water heater, Fridge (electric) Air Conditioners, Converter, Microwave, Electronics (Radio, TV, Et-al) all 120 volt, NOTHING takes 240 volt

So when you are forced to adapt to 30 amps.. THey simply feed the single leg to both sides.

Your wires are designed to pass 50 amps that includes both L-1 L-2, Neutral and I hope safety ground.

Thus when you plug into 30 amps. Your wires are good.

In fact the odds are the neutral can pass a bit OVER 50 amps.. (useful if you use a cheater box and are on a site where you can use a cheater box, rare though those are)

If it helps.. Think of the system as two independent 120 volt systems with a common neutral.. Because.. That is exactly what it is.
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